Power of suggestion - A study conducted in 1997 put 22 people in a creepy theater. Half of the people were told that the place was haunted, and the other half was told the place was under construction. Can you guess which half saw or sensed something paranormal?

Brain problem - It's possible that some of the people who see ghosts have a brain malfunction. While investigating a woman’s epileptic seizures, a neurologist found that applying current to a certain part of her brain made her feel like there was a presence behind her, mimicking her.

The God Helmet - Originally called the "Koren Helmet," it's a device that sends magnetic signals to one's brain. Built to study religious and mystical experiences, it can apparently trigger paranormal experiences.

Maybe it’s just a draft - Cold spots in a house, for instance, are believed to be a sign of paranormal activity. But a sudden change in temperature in a specific spot doesn’t necessarily mean you’ve encountered a ghost.

Maybe it’s just a draft - A study found that ghostly activity was more consistently reported in known "haunted" locations. But environmental factors such as magnetic fields and lighting levels could be to blame.

Exploding head syndrome - This likely happens because the part of your brain responsible for shutting down your body to put you into a sleep state gets a bit confused, and does the opposite instead, putting you in a state of alert.

Sleep paralysis - Paranormal experiences are common during sleep paralysis. This phenomenon occurs when you’re in a dream state, but you're half-awake and unable to move. This is usually a confusing and sometimes terrifying experience.

Why people see ghosts, explained

This is what science has to say about it

Do you believe in ghosts? If so, have you ever seen one? If you answered "yes" to both questions, you are not alone. In fact, a number of surveys found that the majority of people who took part believe in ghosts, with a high percentage claiming that they have seen them.

The belief in the supernatural is an old one. For millennia, humankind have used it as a source of meaning, and continue to do so to this day. But while many people claim to have had paranormal experiences, science also has a word to say about this.

Click through the gallery to find out why people see ghosts, according to science.